I am an admirer of Nesbo's work. His novels are fast-paced, densely plotted, and full of interesting characters. However, The Son brutally exposes his limitations.
This is not a Harry Hole novel. But it might just as well be, as we are on very familiar territory - revenge, unpleasant murders, drug addicts and dealers and police, both noble and corrupt. Instead of Hole, Nesbo gives us Simon Kefas, who is a very pale imitation. He is driven, decent, highly competent, beset by the Demons of his past (Of course!) and about 99% less interesting than Hole.
The Protagonist, however, is Sonny Lofthus (aka The Son). As a side note, this is a book beset by characters whose titles are 'The' Something, so we also have The Twin (evil criminal overlord) and The Mole (pesky cop informer), which is a bit like Lazy Tarantino, a genre which should have its own library classification. Sonny is (by some distance) the weakest element of this novel. When we meet him, he is an imprisoned heroin addict, who hears confessions from fellow inmates, and (in exchange for drugs) confesses to the crimes of others. From the outset, Nesbo is at pains to give Sonny an other-worldly innocence, which makes people talk to him. Sonny escapes and commences a programme of revenge against those who have harmed his family and caused the suicide of his father (also a cop). Suddenly, Sonny becomes Bond / Bourne, coming up with amazing plans (which always work, because people do exactly what Sonny needs them to do to make the plan work), using amazing physical strength and fighting techniques.
Confession - I have not met a huge number of long-term heroin addicts, so this is speculation, but I am guessing that they are neither ace fighters, not capable of executing hugely elaborate plans. Likewise, I am somewhat sceptical about someone who has been in prison since he was 18, but who has an uncanny knack of knowing exactly the right amount of information to implement an elaborate revenge plan.
One can forgive the plot absurdities, though, as par for the course. More grating are the pretensions inherent in Sonny, which really show that Nesbo goes off the rails when he tries to leave his home territory. Is Sonny supposed to be Christ-like in some way, with his innocence, his ability to understand others' thoughts, intentions and weaknesses and his enthusiasm to absolve sin? Is 'The Son', a sledgehammer-subtle reference to 'The Son of God'. It seemed so to me, and if so, the ambition falls squarely over on its face, because there is not only no explanation of why Sonny should have these abilities, but they also serve purely as a plot driver, rather than because Nesbo has anything to say about them. Sonny has amazing abilities, so he can kick more ass and skirt around gaping plot holes. That's it.
Nesbo is very, very good at what he does as an author. However, here he shows that he operates in a very narrow spectrum.